1. Technical Field of the Invention
The invention relates to a performance management method and a system in a cellular mobile packet data network including but not limited to performance analysis, bottleneck analysis, system improvement and dimensioning.
2. Description of Related Art
The performance management of cellular mobile data networks such as General Packet Radio Service (GPRS), Universal Mobile Telecommunication Service (UMTS) and Code Division Multiple Access 2000 (CDMA200O), gets more and more important as the number of subscribers starts to pick up, the traffic on these networks increases and subscribers start to use more and more different applications and services. There is a need for performance management solutions, which makes it easy to find out when there is a performance problem in the network, but it has the same importance to find out the location of the performance problem. Such a performance management system should help the operator in the fields mentioned before, i.e. performance analysis indicates whether users get what they paid for or what they expect, bottleneck analysis presents what the bottlenecks are in the network, system improvement tries to enhance the system such that these problems get eliminated after identifying the causes of performance problems, and dimensioning shows which cells, links, etc need to be re-dimensioned, and how.
In case of a circuit switched service such as voice, it was basically enough to measure the call intensities, call durations and the ratio of blocked calls. In case of packet switched services e.g. Web, Wireless Application Protocol (WAP), File Transfer Protocol (FTP), e-mail, Multimedia Message Service (MMS), etc. the above tasks are not at all trivial, because the end-to-end (or user perceived) performance depends on the interaction of many protocols at different interfaces and on various protocol layers. Furthermore, the use of shared resources leads to rather complicated queuing phenomena, which are difficult to model and analyze.
In current GSM, GPRS, CDMA2000 and UMTS networks, the service area is divided into cells covering limited geographical areas. The aim of the mobile operator should be to provide a constant and ubiquitous high quality service regardless of the location of its subscribers. This is a very challenging task for example because subscribers tend to be distributed non-homogenously across the service area.
Solutions are known for passive measurement based characterization of Internet Protocol (IP) e.g. in “A Passive Method for Estimating End-to-End TCP Packet Loss”, IEEE Globecom 2002, as well as GPRS networks determining user perceived quality using passive monitoring in packet switched systems. For example, in case of GPRS packets on the so-called Gi interface have been captured. The Gi interface connects the Gateway GPRS Support Node (GGSN) with external packet data networks e.g., an Internet Service Provider (ISP). Based on the Gi traffic traces detailed traffic and end-to-end performance analysis results has been delivered to operators. At the same measurement point where Gi traffic can be captured, the messages to/from the Remote Authentication Dial-In User Service (RADIUS) server can typically also be captured. The RADIUS packets can be used to reconstruct user sessions.
Performance counters for GSM/GPRS cells are known from the practice. E.g. Statistics and Traffic Measurement Subsystem (STS) in the Ericsson Base Station System (BSS) records some key radio network events. These counters provide information about the performance and traffic load in specific cells. The following list exemplifies what sort of information the operator can obtain from these counters:                The number of connections successfully established on the Traffic Channel (TCH).        For every cell there are counters for the number of allocation attempts. They are incremented at every attempt to allocate a TCH in a resource type in the cell, to be used for signalling, data or speech, regardless of whether the allocation succeeded or failed.        A counter shows the accumulated number of available (i.e. idle and busy) Basic Physical Channels used for traffic in a cell.        Number of Offered Incoming Calls.        Number of Offered Normal Originating Calls.        A counter is stepped each time the Base Station Controller (BSC) attempts to allocate a set of one or more Packet Data Channels (PDCHS) from the circuit switched domain.        Accumulated number of allocated PDCHS.        The peak number of active PDCHs from the last 15 minutes.        The total number of Radio Link Control (RLC) data blocks transmitted by the Packet Control Unit (PCU) during the measurement period.        The total number of RLC data blocks retransmitted by the PCU during the measurement period.        Accumulated number of Temporary Block Flows (TBFs) per traffic combination of Upload/Download (UL/DL).        Accumulated number of PDCHs carrying at least one TBF per traffic combination of UL/DL and GPRS/EGPRS, where EGPRS stands for Enhanced General Packet Radio Service.        
Counters are collected every 5 or 15 minutes. This is the Basic Recording Period, which can be set by command and is recommended to be 15 minutes. Measurement data for the Basic Recording Period is accessible in the database for two hours.
There is a widespread knowledge about drive tests. In this set-up, special purpose terminals are used, which run a given application. A test user operates the terminal and it runs an application, which is under test.
In case of cellular mobile data networks, the terminal can for example be installed on the board of public transport service bus or a taxi. The application is run repeatedly, and the performance results together with the cell level location of the test are recorded. This way performance results are obtained for the cells, which have been visited during the drive test.
Early experiments quickly showed that in order to efficiently monitor and manage cellular mobile data networks, two type of information is necessary: User perceived end-to-end performance of different applications and information about the resource usage and performance in the different cells. The need for the first type of information is obvious, the reason for requiring this information on cell level is that cells are the basic dimensioning units of cellular data networks, congestion typically occurs because the resources of a particular cell are exhausted, and the performance problem can most often be alleviated by adding additional resources, e.g. a couple of new traffic channels to the problematic cell.
As mentioned before, advanced passive measurement based methods are available to characterize the user perceived end-to-end performance of different applications in case of GPRS networks, but these methods currently work on a whole network basis and it is not currently possible to obtain the key performance indicators on cell level. The problem with the monitoring systems developed for the Internet is that they miss an important abstraction level, which is key to a mobile operator, and that is the level of the mobile subscriber. IP addresses and IP application transactions need to be associated with the mobile subscriber they belong to, which cannot be done with a traditional IP network monitoring system.
There is a set of counters available in the BSS of company Ericsson to obtain performance results on cell level. It is clear from the above list that these counters can be used to understand the cell level performance of circuit switched services but they do not tell much about the user perceived end-to-end quality of service of packet switched applications and services. Other problem with the counters is that different system vendors might implement different counters, which makes it impossible to build a coherent performance monitoring system in a multi-vendor network. Furthermore, the maintenance of these counters puts a significant load on the BSC node. Therefore performance results are available only with a very coarse-grained time resolution. The most important problem with the third performance-monitoring alternative, the drive test is that it is not scalable. It generates additional load over the network and it requires significant time to cover a large area with enough measurements to allow obtaining statistically reliable measurement results, not to mention the difficulty of generating realistic application level traffic patterns in such an artificial use case.
Thus there is a particular need for a passive performance monitoring solution, which provides information about the true, user perceived end-to-end performance of mobile data networks; it provides this information on cell level; it is scalable; and it is vendor independent.
To build such a passive performance monitoring system for cellular data networks is not trivial because the information, which is necessary to be collected, cannot be obtained at a single measurement point.